Backlight unit and display device having the same using two different lights

ABSTRACT

Provided are a backlight unit and a display device having the same. The backlight unit includes a case having an opening, at least one lamp assembly disposed on a side surface of the case and including a light source, an optical transreflective unit on the case, the optical transreflective unit transmitting a portion of first light passing through the opening and reflecting a portion of second light generated from the light source, and an optical sheet including a first diffusion unit on the optical transreflective unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. 119 and 35U.S.C. 365 to Korean Patent Application No. 10-2007-0016654 filed onFeb. 16, 2007, Korean Patent Application No. 10-2007-0027028 filed onMar. 20, 2007, and Korean Patent Application No. 10-2007-0027891 filedon Mar. 22, 2007, which is hereby incorporated by references in itsentirety.

BACKGROUND

The present disclosure relates to a backlight unit, and moreparticularly, to a backlight unit capable of improving opticalefficiency, and a display device having the same.

Recently, various display devices are being developed to meet user'sinformation requirements. Display devices include, for example, liquidcrystal display devices, plasma display devices, organicelectro-luminescent display devices and field emission display devices.

Among such display devices, liquid crystal display (LCD) devices, whichdisplay an image using liquid crystals, are being widely used throughoutindustry thanks to their several advantages such as slimness, lightness,low power consumption and low driving voltage.

The LCD device includes two substrates and liquid crystals interposedtherebetween. A voltage applied across the two substrates controlsorientation of the liquid crystals so that the LCD device displays animage.

The LCD device needs a backlight unit for irradiating light from theoutside because the LCD device is a passive device that cannot emitlight by itself.

However, a light source must be continuously operated because a relatedart backlight unit has to generate light in order for the LCD device todisplay an image, thus leading to an increase in power consumption.

Moreover, it is difficult for the related art backlight unit to providebrightness level beyond predetermined value due to a technicallimitation and an increase in power consumption.

In order to improve optical efficiency, therefore, studies are beingactively conducted on technologies for substituting a light source of abacklight unit lately.

SUMMARY

Accordingly, the present invention is directed to a liquid crystaldisplay device that substantially obviates one or more of the problemsdue to limitations and disadvantages of the related art.

Embodiments provide a backlight unit, which is capable of improvingoptical efficiency using natural light as well as artificial light, anda display device having the same.

Embodiments also provide a backlight unit, which is capable of improvingoptical efficiency using artificial light and natural light depending onbrightness condition of surroundings, and a display device having thesame.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

In one embodiment, a backlight includes: a case having an opening; atleast one lamp assembly on a side surface of the case, the at least onelamp assembly including a light source; an optical transreflective uniton the case, the optical transreflective unit transmitting a portion offirst light passing through the opening and reflecting a portion ofsecond light generated from the light source; and an optical sheetincluding a first diffusion unit on the optical transreflective unit.

In another embodiment, a backlight unit includes: a case having anopening; at least one lamp assembly on a side surface of the case, theat least one lamp assembly including a light source; a diffusion unit onthe case; a cover on the diffusion unit for forming an internal space inthe diffusion unit; a first controller controlling air to be suppliedinto the internal space; and a second controller controlling fluid to besupplied into the internal space.

In a further embodiment, a display device includes: a display panel; anda backlight unit providing light to the display panel. Herein, thebacklight unit includes: a first case having an opening; at least onelamp assembly on a side surface of the first case, the at least one lampassembly including a light source; an optical transreflective unit onthe first case, the optical transreflective unit transmitting a portionof first light passing through the opening and reflecting a portion ofsecond light generated from the light source; and an optical sheetincluding a first diffusion unit on the optical transreflective unit.

In a still further embodiment, a display device includes: a displaypanel; and a backlight unit providing light to the display panel.Herein, the backlight unit includes: a first case having an opening; atleast one lamp assembly on a side surface of the first case, the atleast one lamp assembly including a light source; a diffusion unit onthe first case; a cover on the diffusion unit for forming an internalspace in the diffusion unit; a first controller controlling air to besupplied into the internal space; and a second controller controllingfluid to be supplied into the internal space.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory, and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention

FIG. 1 is an exploded perspective view of a display device according toan embodiment.

FIG. 2 is a sectional view taken along line I-I′ of FIG. 1.

FIGS. 3A and 3B are perspective views illustrating characteristics of anoptical transreflective unit.

FIG. 4A is an exploded perspective view of a display device using firstlight.

FIG. 4B is a sectional view taken along line II-II′ of FIG. 4A.

FIG. 5A is an exploded perspective view of a display device using secondlight.

FIG. 5B is a sectional view taken along line III-III′ of FIG. 5A.

FIG. 6 is a sectional view of a display device according to anotherembodiment.

FIG. 7 is a sectional view of a display device according to stillanother embodiment.

FIG. 8 is a sectional view of a display device according to stillanother embodiment.

FIG. 9 is a sectional view of a backlight unit according to stillanother embodiment.

FIG. 10 is a sectional view of a backlight unit according to stillanother embodiment.

FIG. 11 is a sectional view of a backlight unit according to stillanother embodiment.

FIG. 12 is a sectional view of a display device including a backlightunit according to still another embodiment.

FIG. 13 is a sectional view of a display device according to stillanother embodiment.

FIG. 14 is a sectional view of a display device according to stillanother embodiment.

FIG. 15 is a sectional view illustrating operation of the display deviceof FIG. 14 in a day mode.

FIG. 16 is a sectional view illustrating operation of the display deviceof FIG. 14 in a night mode.

FIG. 17 is a sectional view illustrating operation of the display deviceof FIG. 14 in a night advertisement mode.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentdisclosure, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 is an exploded perspective view of a display device 100 accordingto an embodiment. FIG. 2 is a sectional view taken along line I-I′ ofFIG. 1.

Referring to FIGS. 1 and 2, the display device 100 includes a displaypanel 101 configured to display an image, a backlight unit 110configured to provide external light (hereinafter, referred to as ‘firstlight’) or internal light (hereinafter, referred to as ‘second light’)to the display panel 101, and a top case 150 configured to fix thedisplay panel 101. The first light may include, for example, naturallight provided from the sun or light provided from an artificial lightsource such as an illuminator.

The backlight unit 110 includes a lamp assembly 127, a light guide plate130, an optical reflective-transmissive unit 119 (hereinafter, referredto as ‘optical transreflective unit 119’ simplicity), an optical sheet135, a support main 140 and a bottom case 113 so as to provide thesecond light to the display panel 101.

The lamp assembly 127 includes a lamp 122 and a lamp cover 125. The lamp122 is disposed at one side of the light guide plate 130 and emits thesecond light. The lamp cover 125 is disposed to surround the lamp 122 toreflect the second light emitted from the lamp 122.

The lamp 122 may include, for example, at least one of a cold cathodefluorescence lamp (CCFL), an external electrode fluorescent lamp (EEFL)and a light emitting diode (LED) array board with a plurality of LEDs.

The light guide plate 130 is disposed on the same plane with the lampassembly 127 to provide the second light of the lamp 122 upwardly. Thesecond light emitted from the lamp 122 is directly provided to the lightguide plate 130 or provided to the light guide plate 130 after beingreflected by the lamp cover 125. The light guide plate 130 then providesthe second light upwardly. The light guide plate 130 may be formed ofpoly methyl metharylate acrylate (PMMA). The light guide plate 130 mayhave the shape of a wedge gradually decreasing in thickness away fromthe lamp 122 or may have the shape of a plate with a constant thickness.A plurality of patterns may be disposed on a rear surface of the lightguide plate 130 so as to refract the second light or the first light.

Although it is illustrated that the lamp assembly 127 is disposed at oneside of the light guide plate 130, the lamp assembly 127 may be disposedat two opposite sides, three sides or all the sides of the light guideplate 130.

The optical transreflective unit 119 may be disposed on the rear surfaceof the light guide plate 130. For examples, the optical transreflectiveunit 119 may include at least one of an optical efficiency enhancementfilm, a diffusion sheet and a prism sheet. On a rear surface of theoptical transreflective unit 119, a transparent protective film 121 isfurther provided so as to protect the optical transreflective unit 119from external foreign substances and to support the opticaltransreflective unit 119. The transparent protective film 121 mayinclude, for example, a plastic substrate or a glass substrate.

For instance, the optical efficiency enhancement film may include atleast one of a dual brightness enhancement film (DBEF) and a brightnessenhancement film (BEF). The optical efficiency enhancing film transmitsthe first light but reflects the second light emitted from the lamp 122.

The diffusion sheet may include, for example, at least one of acryl,polycarbonate and polyester. The diffusion sheet diffuses the secondlight or the first light for achieving uniform distribution, and canalso reflect a portion of the second or first light incident on thediffusion sheet. The prism sheet controls a propagation direction oflight. For example, the prism sheet may have prism peaks on one sidethereof.

The optical transreflective unit 119 may include an optical efficiencyenhancement film. Alternatively, the optical transreflective unit 119may include an optical efficiency enhancement film and a diffusion sheetdisposed on the optical efficiency enhancement film. Furtheralternatively, the optical transreflective unit 119 may include anoptical efficiency enhancement film and a prism sheet disposed on theoptical efficiency enhancement film. The optical transreflective unit119 reflects the second light forwardly or transmits the first light.The prism sheet prevents the second light from being randomly reflectedand thus condenses the second light, which makes it possible to improvebrightness.

The optical transreflective unit 119 may selectively transmit or reflectthe second light or the first light depending on the intensity of thesecond or first light.

For example, when the intensity of the second light emitted from thelamp 122 is greater than that of the first light passing through anopening 116 of the bottom case 113, the second light is reflected by theoptical transreflective unit 119 so that it is provided to the displaypanel 101.

On the contrary, when the intensity of the first light passing throughthe opening 116 of the bottom case 113 is greater than that of thesecond light emitted from the lamp 122, the first light, i.e., theexternal light, is transmitted by the optical transreflective unit 119so that it is provided to the display panel 101.

The optical sheet 135 diffuses and condenses the second light or thefirst light provided from the light guide plate 130. The optical sheet135 may include a diffusion sheet, and first and second prism sheets.

The support main 140 supports the display panel 101 while fixing theoptical sheet 135. The support main 140 may have the shape of arectangular frame because it must support the display panel 101.

The bottom case 113, which receives the lamp assembly 127, the opticaltransreflective unit 119, the light guide plate 130 and the opticalsheet 135, is coupled to the top case 150. To provide the first light tothe display panel 101, the opening 116 is provided in the bottom case113, allowing the first light to be incident onto the opticaltransreflective unit 119. Therefore, the first light may be provided tothe display panel 101 through the opening 116 of the bottom case 113 viathe optical transreflective unit 119, the light guide plate 130 and theoptical sheet 135.

The lamp assembly 127 is fixedly coupled to the bottom case 113, and theoptical transreflective unit 119, the light guide plate 130 and theoptical sheet 135 are sequentially received in the bottom case 113.

Thereafter, the support main 140 is received in the bottom case 113, andfixedly coupled to the bottom case 113. The optical transreflective unit119, the light guide plate 130 and the optical sheet 135 can be fixed bymeans of the support main 140.

After the support main 140 is placed on the display panel 101, the topcase is fixedly coupled to the bottom case 113. Accordingly, the lampassembly 127, the optical transreflective unit 119, the light guideplate 130, the optical sheet 135 and the display panel 101, which aredisposed between the bottom case 113 and the top case 150, can be fixed.

The display panel 101 displays an image using the second light or thefirst light provided from the backlight unit 110. For instance, thedisplay panel 101 may include a liquid crystal display panel.

The display panel 101 is divided into two areas, of which one is anactive area for displaying an image and the other is a non-active areadefined in a peripheral region of the active area.

The top case 150 is fixedly coupled to the bottom case 113 such that itsurrounds the non-active area of the display panel 101.

The display panel 101 includes a first substrate 103 having a thin filmtransistor (TFT) array, a second substrate 106 having color filterpatterns, and a liquid crystal layer interposed between the first andsecond substrates 103 and 106. In the display panel 101, a plurality ofpixel regions are arranged in a matrix form in the active area. Each ofthe pixel regions includes a red pixel (R), a green pixel (G) and a bluepixel (B).

The first substrate 103 includes a plurality of gate lines and aplurality of data lines crossing each other.

Each of the pixel regions may be defined in every region where the gatelines cross the data lines. The pixel region includes at least one TFTand a pixel electrode connected to the TFT.

The second substrate 106 facing the first substrate 103 includes red,green and blue color filter patterns are provided, which correspond tothe respective pixel regions defined in the first substrate 103.Further, the second substrate 106 includes light-blocking patternscorresponding to the gate line, the data line and the TFT, and a commonelectrode disposed on each of the color patterns and the light-blockingpattern.

Although not shown, a first polarization film may be disposed on anouter surface of the first substrate 103, and a second polarization filmmay be disposed on an outer surface of the second substrate 106.

Hence, a data voltage is supplied to the pixel electrode by switchingoperation of the TFT provided in each of the pixel regions, and a commonvoltage is supplied to the common electrode of the second substrate 106,so that an electric field is generated between the first and secondsubstrates 103 and 106. This electric field leads to a change inorientations of liquid crystals of the liquid crystal layer to controlthe transmittance of the second or first light provided from thebacklight unit 110, thus displaying a desired image.

The opening 116 of the bottom case 113 may have a size equal to orgreater than that of the active area of the display panel 101. That is,the opening 116 of the bottom case 113 may be at least as great as theactive area of the display panel 101. Accordingly, the first light canbe provided to the active area of the display panel 101 through theopening 116 of the bottom case 113.

The display device 100 having the above configuration may be operated invarious ways.

For instance, if the intensity of the first light is sufficient likedaylight, the lamp 122 of the display device 100 is not used because itis powered off. In this case, only the first light passing through theopening 116 of the bottom case 113 may be used. The first light isprovided to the display panel 101 via the optical transreflective unit119, the light guide plate 130 and the optical sheet 135, so that thedisplay panel 101 displays an image. In the case where the first lightis not generated from the sun but generated from an illuminator, theilluminator may be disposed around the bottom case 113.

The display device 100 may be attached to a transparent support member(not shown). The support member may be a window of a building.

For example, if the intensity of the first light is not sufficient likea cloudy day or night, the lamp 122 of the display device 100 is poweredon to emit light. Internal light emitted from the lamp 122 may beutilized in this case. The second light, i.e., the internal light, isprovided forwardly by means of the light guide plate 150 and the opticaltransreflective unit 119 and then provided to the display panel 101 viathe optical sheet 135, so that the display panel 101 displays an image.

The display device 100 having the above configuration is applicable toany display device displaying an image using the second light or thefirst light. Although the display device of this embodiment is limitedto a twisted nematic (TN) mode liquid crystal panel, it is alsoapplicable to an in-plane switching (IPS) mode display panel. Inaddition, the embodiment can be applied to a reflective ortransreflective display panel.

Since the display device 100 of this embodiment is lightweight and slimand the backlight unit 120 is not always operated but selectivelyoperated according to circumstances, the display device 100 canconsiderably reduce power consumption.

FIGS. 3A and 3B are perspective views illustrating characteristics ofthe optical transreflective unit 119.

Referring to FIG. 3A, the optical transreflective unit 119 transmitsfirst light 165, which is incident on a first surface in a firstdirection, to a second surface. For example, in the case where theoptical transreflective unit 119 has a multi-stacked structure of adiffusion sheet and an optical efficiency enhancement film, the firstsurface is a rear surface of the diffusion sheet and the second surfacemay be a top surface of the optical efficiency enhancement film.Alternatively, the first surface may be a rear surface of the opticalefficiency enhancement film, and the second surface is a top surface ofthe diffusion sheet.

Referring to FIG. 3B, the optical transreflective unit 119 reflectssecond light 166, which is incident on a second surface in a seconddirection opposite to the first direction, toward a first surface. Forexample, in the case where the optical transreflective unit 119 has amulti-stacked structure of a diffusion sheet and an optical efficiencyenhancement film, a portion of the second light 166 emitted from thelamp 122 is reflected by the optical efficiency enhancement film and therest of the second light 166 is transmitted. The transmitted light ispartially reflected by the diffusion sheet and then incident on theoptical efficiency enhancement film. Through repeating such a procedure,most of the second light 166 incident on the optical transreflectiveunit 119 is reflected by the optical transreflective unit 119, and thenincident onto the light guide plate 130.

FIG. 4A is an exploded perspective view of a display device using firstlight. FIG. 4B is a sectional view taken along line II-II′ of FIG. 4A.

Referring to FIGS. 4A and 4B, the first light 165, which passes throughthe opening 116 of the bottom case 113, is provided to the display panel101 via the optical transreflective unit 119, the light guide plate 130and the optical sheet 135.

The transmittance of the first light 165 provided to the display panel101 is changed while the first light 165 passes through the displaypanel 101, so that an image is displayed.

FIG. 5A is an exploded perspective view of a display device using secondlight. FIG. 5B is a sectional view taken along line III-III′ of FIG. 5A.

Referring to FIGS. 5A and 5B, the second light 166 emitted from the lamp122 is reflected by the optical transreflective unit 119, and thenprovided to the display panel 101 via the light guide plate 130 and theoptical sheet 135.

The second light 166 provided to the display panel 101 is changed whilesecond light 166 passes through the display panel 101, so that an imageis displayed.

FIG. 6 is a sectional view of a display device 100 according to anotherembodiment.

Description for like elements, which have been described already in theprevious embodiment of FIG. 1, will be omitted herein.

Referring to FIG. 6, the display device 100 may include at least onesensor 170 configured to sense light quantity of first light 165 emittedfrom an external light source such as the sun and an illuminator. Thesensor 170 may be attached to a side surface of the top case 150. If thedisplay device is attached to a support member (not shown), e.g., awindow of a building, the sensor 170 may be attached to the supportmember in the vicinity of the side surface of the top case 150. Thefirst light 165 may include natural light generated from the sun orartificial light generated from an illuminator.

According to natural law, the light quantity of the sun is varied with alapse of time even during a day, for example, varied depending on a timezone such as daybreak, forenoon, afternoon, evening and night. The lightquantity of the sun may also be varied momentarily depending on anatmospheric state or whether the sun is obscured by cloud. Further, thelight quantity of the sun may differ depending on season or locationeven at the same time zone. Moreover, the light quantity of the sun maybe varied depending on a peripheral condition of the location where thedisplay device is installed, for example, varied depending on whetherthe installation location is overshadowed by surrounding buildings.

The sensor 170 senses the light quantity of the first light 165 variedwith peripheral conditions.

The sensor 170 can also sense the second light 166 emitted from the lamp122. That is, the sensor 170 can sense both the first light 165 and thesecond light 166.

Although not shown, the display device 100 may further include acontroller configured to control the lamp 122 depending on the lightquantity of the sensor 170.

When total light quantity of the first and second light 165 and 166sensed by the sensor 170 is less than a reference value, the controllercontrols the lamp 122 to increase the light quantity of the second light166 emitted from the lamp 122. Therefore, the light quantity of light,i.e., the total light quantity of the first and second light 165 and166, can be always maintained at the reference value. The referencevalue may be light quantity or brightness level set in the display panel101.

When the light quantity of the first light 165 is decreased, the sensor170 senses the decrease in light quantity so that it may increase thelight quantity of the second light 166. Resultingly, it is possible toconstantly maintain the total light quantity of the first and secondlight 165 and 166 provided to the display panel 101.

The sensor 170 may or may not be operated by a user.

The first light 165, which passes through the opening 116 of the bottomcase 113, is incident on the display panel 101 via the opticaltransreflective unit 119, the light guide plate 130 and the opticalsheet 135.

One portion of the second light 166 emitted from the lamp 122 isincident on the display panel 101 as surface light via the light guideplate 130, and the other portion of the second light 166 is reflected bythe optical transreflective unit 119 so that it is incident on thedisplay panel 101.

The transmittance of the first and second light 165 and 166 provided tothe display panel 101 is changed while the first and second light 165and 166 pass through the display panel 101, so that an image isdisplayed.

FIG. 7 is a sectional view of a display device according to stillanother embodiment.

Description for like elements, which have been described already in theprevious embodiments of FIGS. 1 and 6, will be omitted herein.

Referring to FIG. 7, an optical transreflective unit 180 includes adiffusion sheet 183 and an optical efficiency enhancement film 186. Theoptical sheet 183 is in contact with a bottom case 113 and the opticalefficiency enhancement film 186 is in contact with a light guide plate130.

The diffusion sheet 183 is formed of acryl so as to reflect one portionof first light or second light and to transmit the other portion.

The optical efficiency enhancement film 186 may include at least one ofa dual brightness enhancement film (DBEF) and a brightness enhancementfilm (BEF).

The optical efficiency enhancement film 186 transmits one portion of thefirst light and reflects the other portion. A vibration direction oflight reflected by the optical efficiency enhancement film 186 may becoincident with a polarization axis of a first polarization filmdisposed on a rear surface of the display panel 101.

The first light 165, which passes through the opening 116 of the bottomcase 113, passes through the diffusion sheet 183 and the opticalefficiency enhancement film 186, and thereafter is provided to thedisplay panel 101 via the light guide plate 130 and the optical sheet135.

The second light 166 emitted from the lamp 122 is reflected by thediffusion sheet 183 and the optical efficiency enhancement film 186, andthen provided to the display panel 101 via the light guide plate 130 andthe optical sheet 135. Therefore, if the light quantity of the firstlight 165 is sufficient, an image can be displayed on the display panel101 using only the first light 165. Contrariwise, if the light quantityof the first light 165 is not sufficient, an image can be displayed onthe display panel 101 using internal light, i.e., the second light 166,emitted from the lamp 122.

FIG. 8 is a sectional view of a display device 100 according to stillanother embodiment.

Description for like elements, which have been described already in theforegoing embodiments of FIGS. 1, 6 and 7, will be omitted herein.

Referring to FIG. 8, an optical transreflective unit 190 includes adiffusion sheet 193 and a prism sheet 196. The optical sheet 193 is incontact with a bottom case 113 and the prism sheet 196 is in contactwith a light guide plate 130.

The diffusion sheet 193 is formed of acryl so as to reflect one portionof first light or second light and to transmit the other portion.

The prism sheet 196 adjusts a propagation direction of the first andsecond light 165 and 166. For example, the prism sheet 196 may haveprism peaks on one side thereof.

The diffusion sheet 193 and the prism sheet 196 selectively reflect thesecond light 166 from the second lamp 122 toward the display panel 101,and reflect the first light 165, which passes through an opening 116 ofthe bottom case 113, toward the display panel 101.

The diffusion sheet 193 may reflect a portion of the second light 166.The prism sheet 196 condenses the randomly reflected second lightforwardly, thus improving brightness.

Therefore, if the light quantity of the first light 165 is sufficient,an image can be displayed on the display panel 101 using only the firstlight 165. Contrariwise, if the light quantity of the first light 165 isnot sufficient, an image can be displayed on the display panel 101 usinginternal light, i.e., the second light 166, emitted from the lamp 122.

FIG. 9 is a sectional view of a backlight unit 200 according to stillanother embodiment.

Referring to FIG. 9, the backlight unit 200 includes an opticaltransreflective unit 210, a diffusion unit 240, a lamp assembly 230 anda bottom case 220.

The optical transreflective unit 210 and the diffusion unit 240 aredisposed to face each other. The lamp assembly 230 is disposed at leastone side of a region between the optical transreflective unit 210 andthe diffusion unit 240.

The optical transreflective unit 210 has the shape of a sheet or aplate. The optical transreflective unit 210 having the shape of a sheetor plate has a first surface 212 and a second surface 214 facing thefirst surface 212. The second surface 214 of the optical transreflectiveunit 210 faces the diffusion unit 240.

The first light 223 generated from the sun or an illuminator disposedoutside the first surface 212 of the optical transreflective unit 210passes through the optical transreflective unit 210, and thereafter isprovided to the diffusion unit 240. The second light 225 generated fromthe lamp assembly 230 is reflected by the optical transreflective unit210, and then provided to the diffusion unit 240. Accordingly, theoptical transreflective unit 210 transmits the first light 223 generatedfrom the sun or an illuminator, and reflects the second light 225generated from the lamp assembly 230. That is, the opticaltransreflective unit 210 can selectively transmit or reflect the firstand second light 223 and 225.

The optical transreflective unit 210 has a relatively small thickness,and thus it is likely to be bended or deformed downwardly so that it maybe difficult to achieve a flat surface. For example, if the thickness ofthe diffusion unit 240 diffusing the first light 223 and/or the secondlight 225 is about 1 mm or less, the diffusion unit 240 may be bended.If, however, the thickness of the diffusion unit 240 is about 3 mm ormore, light transmittance is reduced and the weight of the backlightunit 200 is increased. Therefore, the diffusion unit 240 may have athickness ranging from about 1 mm to about 3 mm, preferably about 2 mm.

To prevent the optical transreflective unit 210 from being bended, atransparent substrate 242 such as a transparent glass substrate and atransparent synthetic resin substrate, which supports the opticaltransreflective unit 210, may be disposed on the first surface 212 ofthe optical transreflective unit 210.

The diffusion unit 240 diffuses the first light 223, which is generatedfrom the sun or an illuminator and passes through the opticaltransreflective unit 210, and/or the second light 225 generated from thelamp assembly 230. The diffusion unit 240 may be separated from theoptical transreflective unit 210 with the lamp assembly 230 interposedtherebetween.

The lamp assembly 230 generates the second light 225. In thisembodiment, the lamp assembly 230 includes a lamp 232 and a lamp cover234.

The lamp 232 may include, for example, a cold cathode fluorescence lamp(CCFL). Alternatively, the lamp 232 may include an LED array board witha plurality of LEDs arranged. The lamp 232 may be electrically connectedto an inverter (not shown) that supplies a driving voltage to the lamp232.

The lamp cover 234 condenses the second light generated from the lamp232 to propagate the condensed second light toward the opticaltransreflective unit 210 while supporting and receiving the lamp 232. Inthis embodiment, the lamp cover 234 has a substantially U-shape, and mayinclude brass or a synthetic resin of which light reflectance issubstantially similar to that of the brass. The lamp cover 234 includesa first cover 234 a, a second cover 234 b and a third cover 234 c.

The first cover 234 a is in contact with and disposed in parallel withthe optical transreflective unit 210. The second cover 234 b is incontact with and disposed in parallel with the diffusion unit 240. Thethird cover 234 c is connected to both the first and second covers 234 aand 234 b, and contacts the bottom case 220.

The diffusion unit 240 is disposed on the second cover 234 b of the lampcover 234, and thus the diffusion unit 240 can be supported by the lampcover 234.

The lamp assembly 230 may be interposed between at least one diffusionunit 240 and the optical transreflective unit 210. The lamp assembly 230may be provided in plurality between the diffusion unit 240 and theoptical transreflective unit 210 such that they face each other. Forinstance, number of the lamp assembly 230 may be two or four.

The bottom case 220 includes a bottom surface 227 and a sidewall 228.The bottom surface 227 and the sidewall 228 form an internal space inthe bottom case 220. In this embodiment, the optical transreflectiveunit 210, diffusion sheet 240 and the lamp assembly 230 may be receivedin the internal space of the bottom case 220.

An opening 282 is provided in the bottom surface of the bottom case 220such that the first light 223 generated from the sun or an illuminatorcan be provided to the optical transreflective unit 210. Therefore, theopening 282 may be formed in the bottom case 220 except for the bottomsurface 227.

FIG. 10 is a sectional view of a backlight unit 200 according to stillanother embodiment.

Referring to FIG. 10, the backlight unit 200 includes an opticaltransreflective unit 210, a first diffusion unit 240, a lamp assembly230 and a bottom case 220. These elements 210, 240, 230 and 220 havebeen already described in the previous embodiment of FIG. 9, and thusfurther description for them will be omitted herein.

The backlight assembly 200 of this embodiment of FIG. 10 may furtherinclude a second diffusion unit 244 instead of the transparent substrate(see 230 of FIG. 9) in the previous embodiment of FIG. 9. That is, thesecond diffusion unit 244 may be disposed to contact the first surface212 of the optical transreflective unit 210. In other words, the opticaltransreflective unit 210 may be disposed on the second diffusion unit244.

The second diffusion unit 244 supports the optical transreflective unit210 to thereby prevent the optical transreflective unit 210 from beingsagged or bended. The second diffusion unit 244 diffuses the first light223 generated from the sun or an illuminator, thus improving brightnessuniformity of the first light 223. In addition, the second diffusionunit 244 can reflect and diffuse the second light 225 generated from thelamp assembly 230.

The second diffusion unit 244 may have a thickness ranging from about 1mm to about 3 mm, preferably about 2 mm.

The second diffusion unit 244 and the optical transreflective unit 210may be disposed in parallel with the first diffusion unit 240.

In this embodiment, the second diffusion unit 244, the opticaltransreflective unit 210, the lamp assembly 230 and the first diffusionunit 240 may be sequentially received in the bottom case 220.

FIG. 11 is a sectional view of a backlight unit 200 according to stillanother embodiment.

Referring to FIG. 11, the backlight unit 200 includes an opticaltransreflective unit 210, a transparent substrate 242, a diffusion unit240, a lamp assembly 230 and a bottom case 220. These opticaltransreflective unit 210, the diffusion unit 240, the lamp assembly 230and the bottom case 220 have been already described in the previousembodiment of FIG. 9, and thus further description for them will beomitted herein.

Due to the lamp assembly 230 disposed at a side of the backlight unit200, the brightness of the second light 225 generated from the lampassembly 230 becomes lower in a central region of the diffusion unit 250far away from the lamp assembly 230 than an edge region of the diffusionunit 250. The brightness of the first light 223, which is generated fromthe sun or an illuminator and provided through an opening 282 of thebottom case 220, is higher in a central region of the opening 282 of thebottom case 220 than an edge region, i.e., the opening 282 adjacent toone end of the bottom surface 227 of the bottom case 220. Such abrightness distribution is similarly applied to the diffusion unit 250.Consequently, this leads to brightness nonuniformity of the first orsecond light 223 or 225 passing through the diffusion unit 250.

To solve such brightness nonuniformity, in this embodiment of FIG. 11, aplurality of rugged patterns 252 may be disposed on a rear surface ofthe diffusion unit 250 for improving brightness uniformity.

The rugged pattern 252 may have various shapes. For example, the ruggedpattern 252 may have the shape of a triangular pyramid, a quadrangularpyramid or a polypyramid, which protrudes from the diffusion unit 250.The rugged pattern 252 may have a recessed shape from the diffusion unit250.

For example, all the rugged patterns 252 may have the same size butrespective gaps between the rugged patterns 252 may be different fromeach other. Specifically, the rugged patterns 252 may be equal in size,and may be respectively separated by gaps that progressively differ froma central region of the diffusion unit 250 to an edge region.

Alternatively, all the gaps between the rugged patterns 252 may be equalto each other, but the respective rugged surfaces 252 may have differentsizes. Specifically, the rugged patterns 252 may be respectivelyseparated by an equal gap, and may progressively differ in size from acentral region of the diffusion unit 250 to an edge region.

FIG. 12 is a sectional view of a display device including a backlightunit 200 according to still another embodiment.

Referring to FIG. 12, the display device includes the backlight unit200, a display panel 270 and a top case 260.

The display panel 270 is received in a bottom case 220 of the backlightunit 200. The top case 260 is fixedly coupled to the bottom case 220 soas to prevent the display panel 270 from being separated from the bottomcase 220.

The backlight unit 200 includes an optical transreflective unit 210, afirst diffusion unit 250 having the rugged patterns 252, a seconddiffusion unit 244, a lamp assembly 230 and a bottom case 220. Theseelements 210, 250, 244, 222 and 220 have been described already, andthus further description for them will be omitted herein.

The backlight unit 200 of this embodiment in FIG. 12, however, differsfrom the backlight unit of the previous embodiment of FIG. 9 in that theplurality of rugged patterns 252 are provided on the first diffusionunit 250 in comparison with the diffusion unit (see 240 of FIG. 9) ofthe previous embodiment of FIG. 9 and the second diffusion unit 244 isprovided instead of the transparent substrate of the previous embodimentof FIG. 9. The backlight unit 200 of this embodiment in FIG. 12 alsodiffers from the backlight unit of the previous embodiment of FIG. 10 inthat the plurality of rugged patterns 252 are provided on the firstdiffusion unit 250 in comparison with the diffusion unit (see 240 ofFIG. 10) of the previous embodiment of FIG. 10. The backlight unit 200of this embodiment in FIG. 12 also differs from the backlight unit ofthe previous embodiment of FIG. 11 in that the second diffusion unit 244is provided instead of the transparent substrate of the previousembodiment of FIG. 11.

The backlight unit according to the previous embodiments of FIG. 9 to 11may also be employed in a display device instead of the backlight 200 ofthis embodiment in FIG. 12.

FIG. 13 is a sectional view of a display device 300 according to stillanother embodiment.

Referring to FIG. 13, the display device 300 includes a support member310 and a display module 302.

The support member 301 supports the display module 302. In thisembodiment of FIG. 13, the support member 310 may include a transparentsubstrate having a first surface 312 and a second surface 314. Forexample, the support member 310 may be a window that is capable oftransmitting first light 363 generated from the sun or an illuminator tothe second surface 314 from the first surface 312. The support member310 may be a window installed in a building.

The display module 302 may be disposed on the second surface 314 of thesupport member 310. Therefore, the first light 363 generated from thesun or an illuminator passes through the support member 310 and thusprovided to the display module 302. The display module 302 may beattached to the support member 310 using an adhesive member (not shown).For example, the adhesive member is applied between the support member310 and the bottom surface 343 of the bottom case 340 corresponding tothe support member 310, and the support member 310 and the bottomsurface 343 of the bottom case 340 are then pressurized, so that thedisplay module 302 can be attached to the support member 310.

The display module 302 includes a backlight unit, a display panel 350and a top case 342.

The backlight unit may include an optical transreflective unit 328, adiffusion unit 320, a lamp assembly 330 and a bottom case 340.

The lamp assembly 330 includes a lamp 332 and a lamp cover 334. The lamp332 generates second light. One portion of the second light generatedfrom the lamp 332 is directly provided to the optical transreflectiveunit 328, and the other portion is reflected by the lamp cover 334 andthen provided to the optical transreflective unit 328. The lamp assembly330 may be disposed at one side, two opposite sides or all the sides ofthe display module 302.

The lamp assembly 330 may be fixedly coupled to the bottom case 340. Thelamp assembly 330 has been described already, and thus furtherdescription for it will be omitted herein.

The optical transreflective unit 328 may have the shape of, for example,a rectangular plate. The optical transreflective unit 328 may bedisposed on the same plane with the lamp assembly 330 in a sidedirection. The optical transreflective unit 328 transmits the firstlight 363, which is generated from the sun or an illuminator and passesthrough the support member 310, and reflects the second light generatedfrom the lamp assembly 330 toward the display panel 350 in the front.

The diffusion unit 320 transmits and scatters the first light 363passing through the support member 310, thus preventing externalbackground of the support member 310 from being displayed on the displaymodule 302. The diffusion unit 320 may have a size equal to or greaterby about 1.5 times than that of the display panel 350.

In order to prevent the diffusion unit 320 from being discolored due toultraviolet (UV) light contained in the first light 363 passing throughthe support member 310, the diffusion unit 320 may be formed of glassthat is not discolored by UV light. Alternatively, the diffusion unit320 may be formed of synthetic resin that is not discolored by UV lightcontained in the first light 363. Alternatively, a UV blocking film maybe further provided on the diffusion unit 320 so as to prevent thediscoloration of the diffusion unit 320.

The diffusion unit 320 includes a first surface 322 and a second surface324 facing the first surface 322. The first surface 322 of the diffusionunit 320 is in contact with the second surface 314 of the support member310, and a second surface 324 of the diffusion unit 320 is disposed toface the display panel 350.

Optical diffusion patterns 326 are disposed on the second surface 324 ofthe diffusion unit 320. The optical diffusion patterns 326 diffuse thefirst light 363 or the second light incident on the diffusion unit 320.The optical diffusion patterns 326 of the diffusion unit 320 may beformed by etching the second surface 324 of the diffusion unit 320 usingetchant such as hydrogen fluoride (HF).

To improve the optical diffusion efficiency of the diffusion unit 320,the first surface 322 of the diffusion unit 320 and the second surface314 of the support member 310 may be separated from each other by adistance ranging from about 0.5 mm to about 100 mm. In addition, toimprove the optical diffusion efficiency of the diffusion unit 320, thesecond surface 322 of the diffusion unit 320 and the display panel maybe separated from each other by a distance ranging from about 0.5 mm toabout 50 mm.

The second light generated from the lamp assembly 330 may diffuse by theoptical diffusion patterns 326 provided on the second surface 324 of thediffusion unit 320, and is also emitted toward the first surface 322.The second light emitted toward the first surface 322 of the diffusionunit 320 is lost. In order to prevent such a loss, the opticaltransreflective unit 328 may be disposed on a rear surface of thediffusion unit 320. The optical transreflective unit 328 may transmitthe first light 363, which is generated from the sun or an illuminatorand passes through the support member 310, to provide the transmittedfirst light 363 to the display panel 350 while the opticaltransreflective unit 328 reflects the second light generated from thelamp assembly 330 to provide the reflected second light to the displaypanel 350.

The optical transreflective unit 326 and the diffusion unit 320 may befixed to the lamp assembly 330, particularly the lamp cover 334 or aseparate support member (not shown).

The display panel 350 displays an image using the first light 363generated from the sun or an illuminator or the second light generatedfrom the lamp assembly 330. The display panel 350 includes a firstsubstrate, a second substrate and a liquid crystal layer interposedtherebetween. The display panel 350 may be fixed to the bottom case 340.The display panel 350 has been described already, and thus furtherdescription for it will be omitted herein.

Therefore, the optical transreflective unit 328, the diffusion unit 320,the lamp assembly 330 and the display panel 350 are disposed in thebottom case 340. The lamp assembly 330 and the display panel 350 may befixed to the bottom case 340, and the optical transreflective unit 328and the diffusion unit 320 may be fixed to the lamp assembly 330.

In this embodiment of FIG. 13, it is difficult to fix the display moduleto the support member directly only using the aforesaid adhesive memberbecause the display module 302 is too heavy. Accordingly, a ring isconnected to the bottom surface 343 of the bottom case 340, a wire isthen connected to the ring, and the wire is fixed to a ceiling. In thecase where the display module 302 is fixed to the support member 310 inthe vicinity of the ceiling, the ring of the display module 302 may bedirectly fixed to a hooking protrusion provided in the ceiling without awire.

An opening may be provided in the bottom case 340 adjacent to thesupport member 310 to provide the first light 363 passing through thesupport member 310 to the optical transreflective unit 328. Therefore,the bottom case 340 may have the same shape and size as the displaypanel, and it has an internal space therein. The optical transreflectiveunit 328, the diffusion unit 320 and the display panel 350 may bedisposed in the internal space of the bottom case 340. The bottom case340 may have the bottom surface 343 adjacent to the support member 310so that it is fixed to the support member 310 using an adhesive member.

In the daytime, the display device 300 of this embodiment display animage using the first light 363 which is generated from the sun andpasses through the support member 310. Therefore, it is possible toconsiderably reduce power consumption by displaying an image using thefirst light 363 with excellent brightness and brightness uniformity.

The first light 363 generated from the sun passes through the diffusionunit 328 after passing through the support member 310. Thereafter, thefirst light 363 is diffused by the optical diffusion pattern 326 andthen provided to the display panel 350, so that the display panel 350can display an image.

In the nighttime, the display device 300 of this embodiment displays animage using the second light 363 generated from the lamp assembly 330.

FIG. 14 is a sectional view of a display device 400 according to stillanother embodiment.

The display device 400 of this embodiment in FIG. 14 is substantiallythe same as the display device of the previous embodiment of FIG. 13except for a refractive index control unit 420, a cover 410 and a fluid414 filled into the cover 410. Hence, description for like elements,which have been described already in the previous embodiment of FIG. 13,will be omitted herein. Also, like reference numerals and designationsdisclosed herein denote like elements illustrated in the previousembodiment of FIG. 13.

Referring to FIG. 14, the display device 400 includes a support member310, a refractive index control unit 420 and a display module 402.

The display module 402 includes a backlight unit, a display panel 350and a top case 342.

The backlight unit may include a diffusion unit 320, a lamp assembly 330and a bottom case 340.

The refractive index control unit 420 controls a propagation directionof light to display an image on both sides of the display panel 350.That is, as illustrated in FIGS. 15 and 16, first light 464 generatedfrom the sun or an illuminator or second light generated from the lampassembly 330 must be provided to the display panel 350 in order that auser may see an image indoors. On the contrary, as illustrated in FIG.17, third light 466 generated from an indoor illuminator must beprovided to the display panel 350 in order that a user may see an imageon the display panel 350 outdoors. The third light having brightnesspassing through the display panel 350 must be provided to an outdooruser through the support member 310. To this end, the refractive indexcontrol unit 420 controls propagation paths of the first and secondlight or a propagation path of the third light.

The refractive index control unit 420 suppresses optical diffusionfunction by the optical diffusion pattern of the diffusion unit 320 tothereby control an image to be selectively displayed indoors or outdoorswith respect to the support member 310.

For example, the display device 400 displays an image indoors using thefirst light 463 generated from the sun or an illuminator in the daytime.In addition, the display device 400 displays an image outdoors using thethird light 466 generated from the indoor illuminator in the nighttime.

The refractive index control unit 420 may include a cover 410, a fluidcontroller 430, an air controller 440 and an optical sensor 460.

The cover 410 is provided between the diffusion unit 320 and the displaypanel 350. That is, the cover 410 is disposed to surround a rear surfaceof the display panel 350 and a side surface of the bottom case 340between the diffusion unit 320 and the display panel 350. Thisconfiguration of the cover 410 and the diffusion unit 320 form aninternal space. A distance between the diffusion unit 320 and the cover410 contacting the display panel 350 may be in the range of about 0.5 mmto about 5 mm.

The internal space of the cover 410 may be filled with air or a fluid414 under control of the fluid controller 350 or the air controller 440.

The fluid 414 may have the same optical refractive index as thediffusion unit 320. For example, the fluid 414 may include oil.

If the cover 410 is filled with air, the diffusion unit 320 diffuses thefirst light generated from the sun or an outdoor illuminator or thesecond light generated from the lamp assembly 330.

Contrariwise, if the cover 410 is filled with the fluid 414, thediffusion unit 320 does not diffuse the third light that is generatedfrom the indoor illuminator and passes through the display panel 350,but transmits the third light. The reason the diffusion unit 320transmits the third light is that the diffusion unit 320 has refractiveindex substantially equal to that of the fluid 414 filled into the cover410.

Air may be filled into the internal space provided between the diffusionunit 320 and the cover 410 under control of the air controller 440.

The air controller 440 includes an air port 444 and an airopening/closing valve 442. The air port 444 penetrates one sides of thebottom case 340 and the cover 410 to be in contact with the internalspace formed by the diffusion unit 320 and the cover 410. The airopening/closing valve 442 is connected to the air port 444 to open/closethe injection of air. Although not shown, the air controller 440 mayfurther include an air storage tank, which is connected to the airopening/closing valve 442 and stores air. The air opening/closing valve442 may include a solenoid valve operated by an electrical signal. Whenthe air opening/closing valve 442 is opened, the air stored in the airstorage tank is injected into an internal space via the air port 444, orthe air existing in the internal space may be pushed by the fluid 414forcibly filled into the internal space and then stored in the airstorage tank.

The fluid controller 430 includes a fluid port 432, a fluid pump 434 anda fluid storage tank 436. The fluid port 432 penetrates the other sidesof the bottom case 340 and the cover 410 to be in contact with theinternal space formed by the diffusion unit 320 and the cover 410. Thefluid pump 434 is connected to the fluid port 432 and forcibly injectsthe fluid 414 into the internal space via the fluid port 432. The fluidstorage tank 436 is connected to the fluid pump 434 and stores the fluid414.

The fluid 414 may be forcibly filled into the internal space by thefluid pump 434, or the fluid 414 existing in the internal space may bestored in the fluid storage tank 436. That is, when the fluid pump 434operates forwardly, the fluid 414 stored in the fluid store tank 436 maybe forcibly filled into the internal space via the fluid port 432. Atthis point, the opening/closing valve 442 is opened so that the airexisting in the internal space may be stored in the air storage tank viathe air port 444. When the fluid pump 434 operates backwardly, the fluid414 existing in the internal space may be forcibly stored in the fluidstorage tank 436 via the fluid port 432. At this point, theopening/closing valve 442 is opened so that the air stored in the airstorage tank may be filled into the internal space via the air port 444.

The optical sensor 460 senses the first light generated from the sun oran outdoor illuminator. Although not shown, a controller may be disposedbetween the optical sensor 460 and the fluid pump 434. Theopening/closing valve 442, the fluid pump 434 and the lamp assembly 330may be controlled by the controller.

The controller may control the opening/closing valve 442 and the fluidpump 434 depending on a day mode, a night mode or a night advertisementmode, which is selected on the basis of the intensity of the first lightsensed by the optical sensor 460.

FIG. 15 is a sectional view illustrating operation of the display deviceof FIG. 14 in a day mode.

Referring to FIG. 15, the controller senses the intensity of the firstlight such as the sunlight, which is incident from the optical sensor460. If the sensed intensity of the first light 463 is a reference levelor higher, the opening/closing valve 442 is opened and the fluid pump434 operates backwardly. Accordingly, the fluid 414 existing in theinternal space between the diffusion unit 320 and the cover 410 isstored in the fluid storage tank 436 via the fluid port 432. Accordingas the fluid 414 is discharged from the internal space, the air storedin the air storage tank may be filled into the internal space via theopening/closing valve 442 ad the air port 444.

In this case, the first light 463 generated from the sunlight 461 isprovided to the diffusion unit 320 via the support member 310, and isdiffused by the diffusion unit 320. Thereafter, the diffused first light463 may be provided to the display panel 350 via the internal spacebetween the diffusion unit 320 and the cover 410. The display panel 350displays an image to an indoor user using the first light 463.

FIG. 16 is a sectional view illustrating operation of the display deviceof FIG. 14 in a night mode.

Referring to FIG. 16, the controller senses the intensity of the firstlight such as the sunlight, which is incident from the optical sensor460. When the sensed intensity of the first light is less than thereference level and the night advertisement mode is not selected, theopening/closing valve 442 is opened so that the fluid pump 434 operatesbackwardly. Accordingly, the fluid 414 existing in the internal spacebetween the diffusion unit 320 and the cover 410 is stored in the fluidstorage tank 436 via the fluid port 432. According as the fluid 414 isdischarged from the internal space, the air stored in the air storagetank may be filled into the internal space via the opening/closing valve442 and the air port 444.

In this case, the controller drives the lamp assembly 330 to generatethe second light from the lamp 332. The second light is incident on theside surface of the diffusion unit 320 and then diffused by the opticaldiffusion patterns. Thereafter, the diffused second light may beprovided to the display panel 350 via the internal space filled with air461 between the diffusion unit 320 and the cover 410. The display panel350 displays an image to an indoor user using the second light 463.

FIG. 17 is a sectional view illustrating operation of the display deviceof FIG. 14 in a night advertisement mode.

Referring to FIG. 17, the controller senses the intensity of the firstlight such as the sunlight, which is incident from the optical sensor460. When the sensed intensity of the first light is less than thereference level and the night advertisement mode is selected, theopening/closing valve 442 is opened so that the fluid pump 434 operatesforwardly. Accordingly, the fluid 414 of the fluid storage tank 436 isfilled into the internal space between the diffusion unit 320 and thecover 410. Further, the air existing in the internal space is stored inthe air storage tank via the air port 444 and the opening/closing valve442. The controller stops operation of the lamp assembly 330 so that thesecond light is not generated.

In this case, the third light generated from an indoor illuminator isincident on the display panel 350, and converted into an image by thedisplay panel 350. The converted image is displayed to an outdoor uservia the fluid 441 in the internal space, the diffusion unit 320 and thesupport member 310.

When the display device operates in the night advertisement mode, thedisplay device inverts an image, and thus an outdoor user can see acorrect image.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A backlight unit comprising: a case having an opening passing throughthe case; at least one lamp assembly on a side surface of the case, theat least one lamp assembly comprising a light source; an opticaltransreflective unit on the case, the optical transreflective unittransmitting a portion of first light incident upon the opticaltransreflective unit from the exterior through the opening andreflecting a portion of second light generated from the light source;and an optical sheet comprising a first diffusion unit on the opticaltransreflective unit.
 2. The backlight unit according to claim 1,further comprising a light guide plate between the optical sheet and theoptical transreflective unit, the light guide plate transmitting thefirst light in a propagation direction, and transmitting the secondlight by changing a propagation direction of the second light from aside direction to the propagation direction of the first light.
 3. Thebacklight unit according to claim 1, further comprising a protectivefilm on a rear surface of the optical transreflective unit, theprotective film protecting the optical transflective unit from externalforeign substances and supporting the optical transreflective unit. 4.The backlight unit according to claim 1, further comprising a seconddiffusion unit on a rear surface of the optical transreflective unit,the second diffusion unit supporting the optical transreflective unit,diffusing the first light, and reflecting and diffusing another portionof the second light transmitted by the optical transreflective unit. 5.The backlight unit according to claim 4, wherein the each of the firstand second diffusion units has a thickness ranging from 1 mm to 3 mm. 6.The backlight unit according to claim 1, wherein the opticaltransreflective unit comprises at least one of an optical efficiencyenhancement film, a diffusion sheet and a prism sheet.
 7. The backlightunit according to claim 1, the first diffusion unit comprises aplurality of rugged patterns on a rear surface thereof to improvebrightness uniformity.
 8. The backlight unit according to claim 7,wherein the rugged patterns are equal in size, and are respectivelyseparated by gaps that progressively differ from a central region of thefirst diffusion unit to an edge region.
 9. The backlight unit accordingto claim 7, wherein the rugged patterns are respectively separated by anequal gap, and progressively differ in size from a central region of thefirst diffusion unit to an edge region.
 10. The backlight unit accordingto claim 1, wherein the first diffusion unit directly contacts theoptical transreflective unit.
 11. The backlight unit according to claim1, wherein the first diffusion unit is separated from the opticaltransreflective unit.
 12. A display device comprising: a display panel;and a backlight unit providing light to the display panel, the backlightunit comprising: a first case having an opening passing through thecase; at least one lamp assembly on a side surface of the first case,the at least one lamp assembly comprising a light source; an opticaltransreflective unit on the first case, the optical transreflective unittransmitting a portion of first light incident upon the opticaltransreflective unit from the exterior through the opening andreflecting a portion of second light generated from the light source;and an optical sheet comprising a first diffusion unit on the opticaltransreflective unit.
 13. The display device according to claim 12,further comprising: a second case coupled to the first case to surroundthe display panel; and a support member attached to the first case.